Food processing apparatus

ABSTRACT

Cooking apparatus is provided for cooking food products in a continuous manner whereby the moisture formed during the process of cooking is removed from the cooking oil and the time-temperature profile within the cooker along the cooking path may be adapted to substantially conform to a linear or non-linear curve. The apparatus provides a novel process for cooking specialty snack foods having harder bite and/or lowered oil content.

This is a continuation-in-part of copending, commonly assigned, Ser. No.147,808, filed Jan. 25, 1988, pending which in turn is a division ofSer. No. 921,289, filed Oct. 20, 1986, now U.S. Pat. No. 4,738,193,issued Apr. 19, 1988; which in turn is a continuation-in-part of Ser.No. 698,097, filed Feb. 4, 1985, abandoned.

The present invention relates to the field of food processing and, inparticular, to the process of deep frying food snack items.

BACKGROUND

Methods used for deep frying foods on an industrial scale, particularlysnack foods such as potato chips, corn chips, tortilla chips, bananachips and other types of chips or pellets, include batch processing andcontinuous processing. A batch process, for example, to prepare potatochips involves cooking a batch of either washed or unwashed potatoslices in a cooker containing a cooking medium, such as, hot oil, thenremoving the entire batch from the oil for further processing, such asde-oiling, seasoning and so forth. The cooking medium may be oil, lardor other conventional materials. For convenience, hereinafter, thecooking medium will be referred to as oil and the snack food as potatochips, but it is understood that any conventional cooking medium may beutilized and any type of cooked chip may be processed according to theinvention.

Continuous processing, of potato chips, for example, usually involvesconveying the potato slices through a cooker containing hot oil suchthat the length of time the potato slices are in the oil and the oiltemperature are appropriate for the desired potato chip. There areseveral configurations of cookers, the most common one employing linearconveyors. In such a cooker, the slices are continuously placed in theoil at one end of the cooker and advanced under control through thecooker where potato chips are continuously withdrawn from the other end.In either batch or continuous processing, the oil may be heated, forexample, by heaters directly submerged in the oil or by circulating theoil to an external heater and returning the heated oil into the cooker.It will be appreciated that other methods and means of heating may beutilized.

The following is a description, expressed in general terms, of severaltypes of snack items which may be made utilizing the apparatus andteachings of the present invention. The following however is notexhaustive of the types of snack items which may be made in accordancewith the invention since in many instances the properties of snack itemsare unique to the particular manufacturer. Thus, many other types ofsnack items may be made utilizing the apparatus and teachings of theinvention, including chips referred to as "Hawaiian," kettle-cooked,kettle-fried, low-cal, "Deli-style," chocolate-coated, as well asnumerous types of chips unique to geographic locales.

The following descriptions are expressed in general terms, since thereis no standard definition or welldefined parameters for types of snackitems. Thus, the following description is provided to apprise thoseutilizing the invention in general terms of some products to which theinvention applies.

CONVENTIONALLY COOKED SNAK ITEMS

Conventionally cooked snack items, especially potato chips may becharacterized by reference to standardized color charts, oil content,water content, number of folds, clumps, blisters, and the like. Thecapability of a particular type of potato to achieve desirable chipqualities is defined as its chipping quality. Usually, conventionalchips have a oil content in the range of about 32-40% by weight andmoisture content in the range of about 1-4% by weight. Conventionalchips may be cooked either by batch or continuous processing. The mostcommon cooking conditions for a conventional potato chip in a continuousprocess utilize external heating means and continuous oil circulation.The chips are immersed initially into hot oil at a temperature of about360° to 390° F. and conveyed through the cooker such that there is adrop in temperature of the oil along the cooking path. The chips andcooking oil flow concurrently along the cooking path. The cooked chipsare withdrawn from the oil at a temperature of about 320° to 350° F.There is usually a 30° to 45° drop in temperature during the course ofcontinuous cooking of conventional potato chips. In some instances,multi-zone cookers are used wherein the temperature drops along thecooking path in one zone, then rises as the next zone is entered,resulting in a "sawtooth" temperature profile along the cooking path.

Other continuous cooking systems for conventional potato chips includevarious arrangements or configurations of direct fired cookers. Thetimetemperature profile through the cooker can be altered by modifyingthe cooker design but there are severe limitations imposed by the factthat the heat transfer capability is limited by the heat transfersurface available within the cooker. These types of cookers are usuallylarger than external heat exchanger cookers for equivalent productionrates, and more importantly they contain more cooking oil thanexternally heated systems require to cook the same amount of foodproduct. The oil turnover rate, meaning the time in which the equivalentvolume of cooking oil contained in the system is absorbed into the chipsand replaced with fresh oil, is extremely important in maintaining lowfree-fatty acid cooking oil. Another fact effecting cooking oil qualityis the film temperature which the oil is subjected to on the heattransfer surfaces. The internally heated cookers cannot achieve both lowoil volume and low oil film temperatures compared to externally heatedsystems.

However, particularly in the area of potato chip processing, there aretypes of potato chips which vary from what may be considered to beconventional chips in terms of color, texture, oil content, number offolds, salt content and lack of defects. These types of chips arerecognized and preferred by some consumers. These preferences forcertain variations of chips may be related to ethnic or regional habits,to fad or to the consumer's desire to reduce oil intake.

HARD-BITE CHIPS Home-style Chips

There are types of potato chips which have been recognized by theconsumer as having a harder-bite than a conventional potato chip. One ofthese types is usually characterized by the descriptive terms "homestyle" chips. The "home style" chips are usually cooked in a batchprocess but may also be cooked in a continuous process. While precisedefinitions of consumer-recognized chip types are not available, thegeneral characteristics of a "homestyle" chip are that they usually haveharder bite than a conventional chip. "Home style" chips are usuallysliced to standard thickness (about 0.050 in.) but sometimes are slicedto 0.060-0.070 in. or thicker. Sometimes, however, even a soft chip isdesignated as "home style." The potatoes may be washed to remove surfacestarch or cooked unwashed. The slices are cooked at a lower thanconventional chip cooking temperature, i. e., at about 250°-350° F. fora longer period than the cooking time for a conventional chip. Thecooked chips are normally lighter in color than conventional chips andhave an average (32-40% by weight) oil content. Also, whereasconventional chips are normally cooked in vegetable-based oil, "homestyle" chips may be cooked in animal-based oil, which may be solid atroom temperature.

Maui-style Chips

Another type of hard-bite chip which has been recognized by the consumeris the so-called "Mauistyle" or "open kettle" chip. This chip isrecognizable in that it has normal to heavier thickness than aconventional chip, has more color variation and is characterized by aharder bite. Usually, the chips are darker than conventional chips, butcolor is non-uniform. The "Maui-style" chip is processed differentlythan a conventional chip in that the uncooked potato slices are usuallyunwashed or only lightly washed prior to being immersed in the oil. Forconventional chips, the uncooked slices are usually washed prior tobeing immersed in oil in order to remove the surface starch.Furthermore, "Maui-style" chips are usually made by batch processing,although continuous processes exist. The oil content is normal (32-40%by weight) or higher. The time-temperature profile of a batch cookingprocess for a "Maui-style" chip is unlike the conventional chip or lowoil chip in that the oil temperature decreases during the initialportion of the cooking period, then increases during the later portionof the cooking period, thus manifesting a change in the sign of theslope of the time-temperature cooking profile. Its cooking time islonger than a normal chip, usually in the range of 71/2 to 9 minutes.While not intending to be bound by any particular theory, it is believedthat the characteristic time-temperature profile, the particular potatoused and the surface starch on the slices are at least required toproduce a "Mauistyle" chip. Typically, to process "Maui-style" chips,the unwashed or lightly washed uncooked slices are initially immersedinto the hot oil at a temperature of about 290° to 330° F. Over a periodof approximately 2-4 minutes temperature of the oil drops byapproximately 30° , depending on the cooker size, oil volume, batch sizeand surface water. After this period, the cooking will continue duringwhich there is a gradual rise in temperature, usually of about 20° to30° F. Partially due to the fact that a "Maui-style" chip requires alonger cooking time and also because of its unusual time-temperaturecooking profile, the chips are usually made by batch processing sinceconventional continuous cookers produce linear, saw-tooth, or decreasingtimetemperature cooking profiles which are inappropriate for cooking"Maui-style" chips.

LOW-OIL CHIPS

One of these variations of either conventionally-cooked or hard-bitechips is the low oil potato chip, which has been processed by acontinuous cooking system whereby the oil temperature remains relativelyconstant or increases during the entire cooking period, i.e., usually ata temperature range of about 275° to 350° F. The low oil potato chipsare usually cooked for about 2-3 minutes, however, the cooking time willdepend upon the type of potato used, slice thickness, and the cookingtemperature. The oil content of a low oil potato chip may be in therange of about 22-24% by weight or lower, compared to the usual 32-40%of a conventional chip. Thus, a low-oil potato chip as referred toherein will mean a cooked chip having a oil content in the range ofabout 22-24% by weight, or lower. An example of a process for cookinglow-oil potato chips is disclosed in British Patent Specification1519049.

A problem with conventional deep-fried cooking is that when the potatoslices come into contact with the oil, the temperature of the oil isabout 365° F. which will decrease during the stay of the slices in thecooker. On account of the high temperature of the oil, an explosiveboiling takes place in the first part of the cooker, as a result thepressure resulting from the high vaporization rate of the water in theslices causes some of the cell walls to burst. These ruptured cells willat least partially fill with oil when the water contained in the slicesis nearly all removed and consequently the pressure is decreased. Forthis reason, a conventional potato chip will contain a higher proportionof oil compared to a low-oil chip.

However, in the cooking of low oil chips, the low cooking oiltemperature and particular time-temperature curve allow the water to beremoved from the potato cells at a slower rate than with conventionalchips, thus minimizing rupture of the cells while maintaining sufficientvapor pressure to minimize oil entry into the cells. Then surface oil isremoved before the chips cool to minimize absorption of residual surfaceoil.

Lower Oil-content Chip

There is another kind of chip, not necessarily recognizable by color,bite or texture, which, as a result of cooking and post-cookingprocessing, has a lower than normal oil content, but not low enough tobe characterized as low-oil. A lower oil content chip, eitherconventionally-cooked or hard-bite, is desirable by some consumers andin some cases is not as expensive to manufacture as a low-oil chip. Theoil content of a lower oil-content chip is thus in the range of 24-32%by weight.

OBJECTS OF THE INVENTION

It would thus be desirable to provide an apparatus which is readilyadaptable for continuous cooking of various types of snack items,including chips which have previously been cooked by batch processing.

It is also desirable to provide a method and apparatus for improving thequality of conventionally cooked snack items such as potato chips,whereby potatoes of lesser chipping quality may be used to producecommercially acceptable chips. For example, dark or varied colored chipsare a result of presence of reducing sugars which have been convertedfrom starch due to improper storage conditions, growth condition and theparticular variety of potatoes. It is thus advantageous to provide anapparatus whereby the cooking conditions are readily varied in thecooker to adapt to the characteristics (such as, sugar content) of aparticular supply of potatoes in order to produce the consistent andlighter chip color.

It is also desirable to be able to vary the oil content of the snackitem. For example, low oil potato chips require a specialized process,but oil content may also be varied by the oil temperature which, inpart, is governed by the time-temperature relationship. It is thusdesirable to be able to readily vary the cooking oil temperature profilein a cooking apparatus, since cooking time may be readily varied.

It is therefore most desirable to provide one apparatus which may beadjusted or programmed to cook all types of snack items as well as dealwith variations in the raw food item, including the sliced form in whichthey are cooked (sliced, shoestring, etc.).

It is therefore an object of the present invention to provide anapparatus for continuous processing of cooked food products which willprovide a wide variety of time-temperature profiles.

It is another object of the present invention to provide an apparatuswhich provides an adjustable time-temperature cooking profile toaccommodate variations in the solids content, sugar/starch content andother characteristics in raw potatoes in order to achieve a uniformand/or improved product.

It is another object of the present invention to provide a method andapparatus for use therewith, for cooking food products in at least fourtemperature zones wherein the first two zones are characterized by asteady decrease in temperature and the final two or more zones arecharacterized by an overall increase in temperature wherein thetemperature rises and then drops slightly in each zone.

These and other objects of the present invention will be apparent fromthe following description of the preferred embodiments.

SUMMARY OF THE INVENTION

The present invention provides a method and cooking apparatus forcontinuous processing of food products, particularly snack foodproducts, wherein such apparatus provides cooking zones along thecooking path in the cooking apparatus which are adjustable intemperature and which apparatus further provides a cooked food productwith reduced free-fatty acid by utilizing a reduced water-content(therefore, with less hydrolysis) in the cooking medium, low exposure toatmospheric oxygen, reduced total volume of cooking medium and generallyreduced cooking temperature.

The present invention generally provides a method for cooking snackfoods wherein the time-temperature cooking profile may have at least onechange in sign of the slope and wherein cooking conditions are performedunder low oxygen-atmosphere, low watercontent cooking medium, low volumecooking medium, and results in low free-fatty acid content in the cookedsnack foods. Lowered cooking temperatures are also a feature of thepresent invention.

In a preferred embodiment, a cooking apparatus is provided wherein thefood products are conveyed along a cooking path through a hot oil baththrough four or more successive cooking zones. The cooking profiles inthe third, fourth, and successive zones are controlled by appropriateinlets and outlets to provide at least one change in sign of the slopeof the time-temperature curve within each zone. As an example, preferredcooking profiles are described hereinafter, but it will be realized thatany desired profile may be accomplished having a change in sign of theslope of the time-temperature curve or a continuous temperature drop, inany of the cooking zones.

In the first zone at the beginning of the zone a preferred temperatureis in the range of about 300° to 310° F. and the temperature slowlydrops along the cooking path through the zone to a final preferredtemperature in the range of about 245° to 255° F. with no increaseoccurring in the temperature along the path through the first zone. Thesecond cooking zone is also characterized by a decrease of temperaturealong the cooking path through the zone with no increase in temperaturealong the path where the preferred beginning temperature is in the rangeof about 245° to 255° F. and the preferred final temperature is in therange of about 235° to 245° F. The third zone is preferablycharacterized by two or more sub-zones. The preferred final temperatureat the end of the third zone is in the range of about 290° to 300° F.where the cooked products are withdrawn from the hot oil. Within eachsub-zone there is a time-temperature cooking profile along the cookingpath characterized by an initial increase in temperature followed by adecrease in temperature with a net difference between the temperature atthe beginning of the sub-zone and the end of the sub-zone typicallybeing about 10° to 40° F. The peak temperature in each of the sub-zonesis preferably within about five degrees of the temperature at the end ofeach respective sub-zone. The first two zones plus the two or moresub-zones comprise the four or more cooking zones according to apreferred embodiment of the present invention.

In a preferred embodiment, a cooking apparatus is provided which resultsin a particularly low freefatty acid (FFA) level in the cooked product,utilizing a low volume of oil. In this particular embodiment the entirecooker is contained within a sealed hood, thereby minimizing contact ofatmospheric oxygen with the hot oil. Additionally, oil is recycled in aplurality of cooking zones, wherein each zone may be maintained at ahigher or lower temperature from the other zones. The recycled oil isdewatered in a location exterior to the cooker by contact with a dryinert gas (such as nitrogen or carbon dioxide), which removes water fromthe oil by hydration of the inert gas bubbles. Removal of water from thecooking oil in this manner is an advantage since the presence of waterin the oil is a major cause of FFA buildup. Lowering FFA content of thecooking oil lowers FFA content in the cooked product, thereby improvingshelf life (delaying onset of rancidity), taste and digestibility.

One of the advantages of the present invention is that it efficientlydeals with the problem of highmoisture oil. Cooking oils at 275° andhigher can contain water. The water enters the oil from both the surfaceof the food product and from the water being driven out of the foodproduct during cooking. The mechanism of water being contained in oil ata temperature above its boiling point is a result of several phenomena.As heat is transferred from the hot oil to the colder water the surfaceof the water mass changes state from liquid to vapor. In doing so, alarge quantity of heat is required, specifically 970BTU/pound of waterat atmospheric pressure. As this change of state occurs the surface ofthe liquid water mass becomes enveloped by steam which is a poorconductor of heat, as compared with liquid water. This steam blanketfurther reduces the heat transfer from the oil to the water mass. If,however, the oil is sufficiently agitated so as to remove the steamblanket from the water mass, or more important if the water mass isdivided into smaller particles, then the heat transfer rate is greatlyincreased and rapid change of state from liquid water to steam occurs.

It is desired that as much of the water as possible be removed from theoil before entering the suction of a circulating oil pump, because thereduced pressure and turbulence that occur in the pump suctionaccelerate the process of water removal from the oil and cavitation ofthe pump occurs, resulting in damage to the pump. Since most pumpsoperate on a volumetric basis the mass flow of the oil is reduced sincemuch of the volume being pumped is replaced by vapor. This situation hasserious effects in the heat exchange system due to reduced oil flowrates and local hot spots on the heat transfer surface due to thepresence of vapor instead of oil. The cavitation may at times become sosevere that oil circulation ceases completely.

It is further desired that as much water as possible be removed from therecirculated cooking oil before the oil is reheated at the external heatexchanger, since this would reduce hydrolysis (resulting in FFAproduction) which might occur when the oil is reheated.

Also, since a minimum system oil volume is of primary importance inmaintaining low free-fatty acid in the oil, systems which remove waterfrom oil but require large volumes of cooking oil, are not practical.Therefore, the present invention provides apparatus, described in detailhereinbelow, which utilize a low volume of cooking medium (e. g., oil)while also removing water from the cooking medium to reduce FFAproduction.

Thus, in yet another embodiment, the present invention provides anapparatus for continuous processing of food products comprising acontainer adapted to accommodate hot oil, a conveying means forcontrolled advance of food products along a predetermined path withinthe container, heat exchanging means external to the container adaptedfor heat exchange with oil communicating with the container, means forwithdrawing high-moisture oil from the container, distributing means forrecirculating oil withdrawn from the container through a plurality ofinlet means disposed along the path wherein the inlet means comprisemeans for mixing the recirculated high-moisture oil with oil incommunication with the heat exchanging means, and means forproportioning the relative amounts, such as a valve, of the recirculatedhigh-moisture oil and the oil communicating with the heat exchangingmeans flowing into the mixing means.

In another embodiment, there is further included a de-oiling systemintegrated with the cooker which somewhat de-oils the cooked product,resulting in a lower-oil content food product as described above. Thede-oiler is provided by a conveyor belt within the cooker which removesthe cooked product from the oil bath and, while on a second conveyor,available atmosphere generated within the enclosed cooker is exhaustedthrough or around the cooked product to drain and de-oil the product.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a preferred apparatus according to thepresent invention wherein the cooker is in a sealed hood.

FIG. 1A is a detailed view of end chamber 102 in FIG. 1 along sectionline A.

FIG. 1B is a detailed view of the cooking zone at sump 93 in FIG. 1along section line B.

FIG. 1C is a detailed partial front elevational view of strainers 95 and96 shown in FIG. 1.

FIG. 1D is a detailed side elevational view of the strainer shown inFIG. 1C.

FIG. 1E is a side elevational view of a de-watering apparatus which maybe used in conjunction with the cooking apparatus shown in FIG. 1.

FIG. 1F is a schematic block diagram showing the preferredinterconnection between a cooker as shown in FIG. 1 with a de-wateringapparatus as shown in FIG. 1E and heat exchangers for heating cookingoil.

FIG. 2 is a schematic illustration of another cooking apparatusaccording to the present invention.

FIG. 2A is a detailed view of the mixing apparatus 31A and 32B in FIG.2.

FIG. 3 is a schematic drawing of a third apparatus according to thepresent invention.

FIG. 3A is a detailed view of the mixing apparatus 56A and 57B in FIG.3.

FIG. 4 is a plot of a typical time-temperature curve and time-Bturequired curve for the cooking of "Maui-style" potato chips.

FIG. 5 is a schematic drawing of a preferred apparatus according to thepresent invention wherein there are five cooking zones.

FIG. 6 is a plot of a typical time-temperature cooking curve for cooking"hard-bite" chips in a five zone cooker such as that shown in FIG. 5.

FIG. 7 is a plot of a typical time-temperature cooking curve for cookingof "hard-bite" chips in a seven zone cooker.

FIG. 8 is a plot of a time-temperature cooking curve for cooking in afive-zone cooker wherein there is only one temperature rise and fallduring the last three zones.

FIG. 9 is a plot of another time-temperature cooking curve for cookingin a five-zone cooker.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 there is shown a preferred embodiment of anapparatus according to the present invention equipped with means forvarying the localized cooking oil temperature along the cooking path sothat the time-temperature profile along the cooking path may be made tosubstantially conform to a predetermined time-temperature curve, andparticularly to a time-temperature curve having at least one change inslope. The cooking apparatus shown in FIG. 1 also provides an enclosedhood to minimize contact of hot oil with atmospheric oxygen, providesfor a low volume of cooking oil and a low-water content in the oil, allof which contribute to a low-FFA-content cooked product.

The cooking medium used in the cooking apparatus shown in FIG. 1 isheated by means of one or more heat exchangers (not shown) locatedexternally to the cooker. For example a single heat exchanger may beused to heat the entire volume of the cooking medium, a series of heatexchangers may heat the entire volume, or a plurality of circulationloops, controlled by valving, each with a separate heat exchanger may beutilized.

Referring to FIG. 1 container 82 is shown in a split side elevation. Theleft side of the elevation is shown in the upper portion of the figureand the right side of the elevation is shown on the lower portion of thefigure. Container 82 holds the cooking oil, however, in this instance,the oil is contained within a volume substantially sealed from theatmosphere by the walls and roof of the insulated enclosure 80.Container 82 will be filled with oil so that the oil level is below thelower edge of baffle 81, but high enough so that the boil level (towhich the oil rises when heated) is above the lower edge of baffle 81,thereby sealing the inner portion of the container 80 during cookingfrom the atmosphere at one end. At the other end where the cooked foodproduct exits the cooker by airlock device which minimizes the exposureof the interior of enclosure 80 to the oxidizing atmosphere.

Recirculated oil from the heat exchanger (not shown) exterior tocontainer 82 is introduced through conduits 84 which flow into a baffledinlet 85. Oil is also introduced through conduits 86 which flow throughinlet 88 and through conduits 87 which flow through inlet 89. Oil iswithdrawn from the container 82 through conduits 90A, B and C forheating and circulation.

The raw prepared food product, is dispensed from conveyor belt 91 anddropped into the hot oil and conveyed along the cooking zone by means ofa plurality of rotating paddles 92 which dunk, separate, agitate andcontrol the advance of the food product as it is cooked. As shown, thereare two sumps 93 and 94 along the cooking path wherein oil flows fromthe cooking zone through exit pipes 90A and 90B, respectively, whilefresh oil and/or recycled oil is introduced through inlets 88 and 89,respectively. As shown, this is done by use of self-cleaning strainers95 and 96, which allow the exit of oil without fouling the sumps 93 and94 with chips. By controlling the temperature of oil which entersthrough inlets 88 and 89, respectively, cooking zones may be establishedwith different temperatures. For example, the chips may be cooked in onetemperature range as they pass from their initial immersion in the oilnear conveyor 91 to sump 93. Then a second cooking temperature range maybe utilized as the chips pass from sump 93 to sump 94. A thirdtemperature range may be utilized between sump 94 and sump 97.

After the chips pass sump 94, they will contact conveyor 98 where theyare transferred through the final cooking zone in the hot oil by meansof a flighted submerger-type conveyor 98 which holds the chips below thesurface of the oil while controlling their advance through the cooker.The cooked chips are then removed from the cooker by means of a takeoutconveyor 99 which deposits the chips onto a de-oiling conveyor 100. Thede-oiling conveyor is of open-weave mesh construction and is locatedwithin a chamber 102 which contains an opening 103 to an exhaust fan.Drainage of oil from chips along conveyors 99 and 100 is enhanced byheat, which may be provided by flow of cooker exhaust gases and/or byoverhead heaters 110. The cooked, de-oiled chips are then deposited intoa rotary discharge airlock drum 83 and exit the cooker through chute104.

Trough 130, when filled with oil or other liquid, forms a liquid sealfrom the atmosphere.

Referring to FIG. IA, there is shown a section view through section lineA of FIG. illustrating in more detail the interior of chamber 102. Thereis shown a fines removal auger 101 which removes fine particles from theoil prior to drainage of oil through drain 90D. The fines are removedthrough the upper end of auger 101 into container 105. The oil iscollected in container 106 and returned for re-use in the cooker. Theexhaust duct 103 is also shown as accommodating mist eliminator 107.

Still referring to FIG. IA, there are illustrated liquid-seals for thesides of hood 80. Filling troughs 130 with oil or other liquid seals theinterior of the cooker from the outside atmosphere. The troughs 130 onboth sides of the hood 80 are joined as a continuous trough around atleast three sides of the cooker. Interior longitudinal passages 131 areadjustable raceways for bypass of interior atmosphere around the chipson the deoiling belt 100.

Referring to FIG. IB, there is shown a detailed view of the cooking zoneat sump 93 in FIG. 1, taken along section line B. It can be seen thatsump 93 is sloped downwardly toward the center of the cooking zone. Atthe bottom of sump 93 is the drain pipe 90A, disposed below drum 95.

Referring to FIG. 1C there is shown a partial front elevational view ofa strainer 95 (or 96) as described in connection with FIG. 1. Thestrainer comprises an outer perforated shell 200 affixed to hollowrotatable shafts 201 and 202. In the interior of the drum defined by thecylindrical strainer 200 is a fixed baffle 203. The perforated strainer200 allows oil to pass therethrough, while the baffle 203 provides aphysical barrier to separate the upwardly and downwardly flowing streamsof oil which pass through the strainer 200.

Referring to FIG. 1D there is shown a detailed side elevational view ofthe strainer 95 of FIG. 1C. As shown in FIG. ID the cooking food productis moving to the right and the strainer is rotating clockwise. As thecooking oil and food product come in contact with the strainer surface200 the hot oil flows downwardly into the drain sump (not shown). Thefood product 210 is carried by the rotating action of strainer 200 andis transported along the cooking path. To prevent accumulation of thecooking food product at the downstream side of the strainer 200, theupward flow of incoming fresh and/or recycled cooking oil breaks up anyaccumulated mass of product, thereby preventing clogging and stoppage ofthe strainer 200. Fixed baffle 200 serves to physically divide theupwardly and downwardly flowing streams of oil. As shown, baffle 203 hasan angular portion to direct the upwardly flowing oil towards the mostlikely points of potential accumulation of food product.

Referring to FIG. 1E which is a side elevational view of a de-wateringdevice. The de-watering device is adapted to receive cooking oil fromthe cooker through inlet 220. Inlet 220 will receive oil, for example,from drain conduits 90A, 90B and 90C shown in FIG. 1. An inert gas isintroduced through gas inlet 221 and the bubbles of gas are intimatelymixed with the incoming oil by passage through a tortuous path definedby a plurality of baffles 222. The bubbles come to the surface 223 ofthe oil and exit the de-waterer through stack 224. The oil, now beingsubstantially de-moisturized, flows out into pump 225 where it isdischarged through outlet 226 for heating and recycling.

Referring to FIG. 1F there is shown a schematic diagram of theinterconnection between a cooker such as shown in FIG. 1 with ade-watering apparatus such as shown in FIG. 1E and one or more heatexchangers. From cooker 230, oil is withdrawn from different zonesrespectively through lines 231, 232 and 233. The withdrawn oil is thenintroduced into de-watering apparatus 234 where it is mixed with aninert gas such as described hereinabove. Additional makeup oil may beadded into the de-waterer 234 through line 235 from an oil storagesource (not shown). The demoisturized oil is then passed through line236 to heat exchanger 237. A plurality of heat exchangers may beutilized, preferably corresponding to the number of heating zones withinthe cooker 230. Therefore as shown in the figure, optional heatexchangers 238 and 239 may also be utilized. The reheated oil passesfrom heat exchanger 237 (and optionally from heat exchangers 238 and239) through line 240 to be returned to the cooker. The oil is returnedthrough inlets 241, 242A and 243A which, respectively, introduce heatedoil into the different cooking zones within the cooker. If heatexchangers 238 and 239 are utilized then each heat exchanger may beseparately utilized to introduce oil into respective inlets 241, 242Band 243B. In such case, inlets 242A and 243A are unnecessary and thusmay be omitted or closed to line 240 by appropriate valves (not shown).

The cooking apparatus according to the present invention may be utilizedas the continuous cooking component in a food processing system. Thus,the cooking apparatus according to the present invention may be used inconjunction with a slicer or combination of slicer and washer locatedupstream of the cooker. The slicer may be located upstream of the cookerwhereby the sliced raw food products are conveyed by appropriate meansand deposited into the entrance end of the cooker. Alternatively, theslicer may be disposed above the entrance end of the cooker whereby theslices of raw food are dropped directly into the hot oil. The slicer maybe adapted with a washing apparatus which may be optionally used, toprovide the versatility of cooking washed raw slices of potatoes forconventional potato chips, or unwashed raw potato slices such as"Maui-style" or country style chips. Washing apparatus is commerciallyavailable whereby a washing step may be used o omitted without changingequipment.

Referring to FIG. 2, there is shown a schematic diagram of anothercooking apparatus according to the present invention. Container 10 isadapted for accommodating hot cooking oil. The raw food product isintroduced into the container in the area indicated by arrow 11. As thefood products are cooked, they will usually float and eventually comeinto contact with conveyor 12 which with oil velocity in zone A controlsresidence time. Conveyor 12 also transfers the chips into zone B where aplurality of rotating paddles 13 dunk, separate, agitate and control theadvance of the chips. The forward velocity of the cooking oil is usuallyfaster than the paddle speed so the paddles 13 hold the chips back toprovide uniform cook time. After the chips pass through the agitatedzone B they will contact a conveyor 14 which transfers them into thefinal zone C where they are conveyed through the hot oil by means of aflighted submerger conveyor belt 15 which holds the chips below thesurface of the oil while controlling their advance through the cooker.The cooked chips are then removed from the cooker by means of take-outconveyor 15A and excess surface oil is drained at the same time from theproduct. It may be seen that the total cooking time is determined by theperiod it takes for a particular chip to traverse the length of thecontainer 10 and the temperature profile within the container isdetermined by the temperature gradient, if any, along the cooking pathin container 10.

Fitted inside the transfer conveyors 12 and 14 are adjustable heightweirs 12A and 14A, respectively, that control the oil level in zones Aand B, respectively. Since the oil entering a zone must equal the amountof oil leaving the same zone, this weir maintains zone oil level whileallowing the excess oil volume to flow from zone A to zone B, and zone Bto zone C. This feature allows much greater flexibility in setting theoil circulation rates in each zone to accomplish the desired temperatureprofile.

During the process of cooking potato chips, the initial zone within thecooker produces a high level of water in the oil as a result of rawproduct surface water removed from the product in the cooking process.Reaction of water with oil (hydrolysis) shortens the useful life of theoil, so water should be removed as rapidly as possible from the oil.

The apparatus shown in FIG. 2 is equipped with means for varying thelocalized cooking oil temperature at various points along the cookingpath so that the time-temperature profile along the cooking path may bemade to substantially conform to a predetermined time-temperature curve,and particularly to a time-temperature curve having at least one changein slope. A change in slope in a curve means there is at least one pointin the timetemperature profile where the temperature changes fromdecreasing to increasing or from increasing to decreasing.

Referring again to FIG. 2, container 10 is adapted with oil dischargelines 17A, 17B and 17C. The oil which discharges through line 17A duringthe cooking process will contain a substantial amount of water, withsomewhat less water being present in the oil discharging through line17B. The oil discharge through line 17C will usually contain arelatively small amount of water, if any, since the cooked chips, at theend of the cooking process, contain little water. The oil through line17C is pumped via pump 18 into heat exchanger 19 where the oil isreheated for recirculating into the container 10. The heat exchanger 19may be fuel-fired or heated in any other available manner. The reheatedoil exiting from heat exchanger 19 through line 20 is then distributedthrough a network of lines 21, 22, 23 and 24 into container 10. However,before entering container 10 the recirculated hot oil in lines 22 and 23is first mixed with high water containing oil from lines 17B and 17A,respectively. The proportioning of the mixtures of the oil from lines 22and 17B is controlled respectively through valves 25 and 26 and theproportioning of oil from lines 23 and 17A controlled respectivelythrough valves 27 and 28. Appropriate pumps 29 and optional filter 30are provided. The apparatus for mixing the high water containing oil andthe hot oil comprises components 31A, 11B, 32A and 32B.

The detail of 31A, 31B, 32A and 32B is shown in FIG. 2A. The high watercontaining oil is forced through a distribution manifold and through aplurality of jets 32A. The hot oil from the heat exchanger 19 is alsoforced through a distribution manifold and through a plurality of jets32B which is larger in diameter and concentric to jet 32A. The rapidcontact and intimate mixing of the high-moisture containing oil with thehot oil will cause the dispersed water droplets to vaporize and flashfrom the oil, thereby lowering the moisture content of the oil as itreenters tank 10. As shown, jets 32A and 32B may be disposed at an anglewith respect to the oil flow within the tank 10. Alternatively, highwater containing oil may be forced through jets 32B and hot heatexchanger oil may be forced through jets 32A, thereby reversing theroles of the jets.

The relative flow rates of hot oil through jet 32B and cooler oilthrough jet 32A will control the average temperature of the oil withinthe vicinity of each inlet 32B into container 10. Thus, by disposing aplurality of inlets 32B along the cooking path within container 10 thetime temperature profile along the cooking path may be controlled tosubstantially conform to any predetermined curve. Various temperaturemonitoring means, such as thermocouples, may be disposed at advantageouspoints to monitor the temperature characteristics of the oil. Exemplarytemperature monitoring units 33 are shown in FIG. 2.

FIG. 3 shows another apparatus according to the present invention. Adifference is that in FIG. 3, there are two streams of oil flowing inopposite directions, both of which drain into sump 40 in the tankcomprising sections 41A and 41B. The sliced raw food products aredispensed from conveyor belt 42 and dropped into the hot oil into tank41A. Chips are conveyed through cook zone A by a combination of forwardoil velocity and the speed of submerged conveyor 43. Conveyor 43 alsoserves to separate the chips from the oil exiting through oil outlets 46and sump 40. This positive means of separating the chips from the oilexiting the fryer provides greater flexibility in adjusting oil flowrates through intermediate inlets and outlets 56A, 56B and 46 which asnecessary provide the desired time-temperature curve. As the chips leavezone A, they are engaged by the initial portion of conveyor 44 whichpositively conveys the chips through both zone B and zone C by aplurality of suspended positioning flights 44A. Since the chips in zoneB may still contain sufficient moisture that confinement in a restrictedarea would result in the formation of clumps of chips that are cookedtogether, the belt portion of conveyor 44 is kept above the oil leveland only the positioning flights are used to control the chip movement.When the chips reach zone C, the conveyor belt 44 is offset downwardlyto reduce the product space and then submerges the chips under thesurface of the oil where cooking is completed.

Positioning flights 44A also serve as wipers to prevent build-up ofstarch or product fines on the tank bottom. In this application flights44A are similar to that shown in U.S. Pat. No. 3,472,155. Flights mayalso be attached to belt 43 to provide similar wiping action in Zone A.

The cooked chips are conveyed onto take-out conveyor 45 and dischargedfrom the cooker. The oil in tank 41B flows downwardly into sump 50 tothe left whereas the oil in tank 41A flows downwardly into sump 40 tothe right in FIG. 3 as shown. The high water containing oil in zone A isconfined substantially to tank 41A and is discharged through a networkof lines 46 and pumped by pump 47 for recirculating into tank 41A and41B through lines 48 and 49. The substantially moisture-free oil fromzone B and C draining into sump from tank 41B is separated from the oilin the sump 40 draining from 41A by baffle 50. This substantiallymoisture-free oil is withdrawn through line 51 by pump 52 into heatexchanger 53 where the oil is reheated to an appropriate temperature.The reheated oil is then recirculated into tank 41A through the networkof lines 54 and into tank 41B through line 55. The hot oil in lines 54is mixed with the high water containing oil from lines 48 and the hotoil from line 55 is mixed with high water containing oil from line 49 bythe mixing apparatus 56A and 56B, shown in greater detail in FIG. 3A.

Referring to FIG. 3A, the hot oil from the heat exchanger is passedthrough a distribution manifold and through jets 57B. The high watercontaining cooler oil is passed through the distribution manifold andthrough jets 57A which are concentric with jets 57B. The rapid contactof the hot oil and the cooler high water containing oil causes intimatemixing and sudden expansion of the water droplets and flashing off thewater vapor. As shown, the inlet jet 57B is orthogonal to the flow ofoil within tanks 41A and 41B.

The localized temperature along sections of tank 41B may be controlledby disposing along the cooking path within tank 41B inlet jets 58 whichcontain reheated oil from heat exchanger 53 and which flash off moisturein oil before it reaches sump 40 and pump 52. Various temperaturecontrol means such as thermocouples, not shown, may be appropriatelylocated along various lines and locations in the tank to control thelocalized temperature within each tank 41A and 41B. The relative flow ofhot and cold oil through the various lines may be controlled by variousvalves 60.

Downstream from the cooker there may be used a defatter apparatus, suchas that described in Swedish Patent 833,714 or U.S. Pat. No. 3,627,535,whereby the cooking system will make low oil potato chips.

Also located downstream from the cooker may be conventional seasoningand packaging apparatus.

Referring to FIG. 4, there is shown a plot of a typical time-temperatureprofile and time-Btu required profile for the cooking of "Maui-style"potato chips. Although these curves were determined from a batch stylecooker, these time-temperature profiles may be substantially reproducedusing a continuous cooker as shown in FIGS. 2 or 3. As may be seen inFIG. 4, the time-temperature profile for cooking "Maui-style" chipsshows an initial cooking temperature of about 330° F. which graduallydecreases for approximately 3 to 31/2 minutes to about 304° F. After 3to 31/2 minutes, the temperature then increases, and gradually increasesover the next 41/2 minutes to a final temperature of about 324° F., atwhich time the cooked chips are removed from the oil and the oiltemperature is allowed to increase to 330° F. before the next batch isstarted.

Referring to FIG. 5, there is shown a schematic diagram of a preferredcooking apparatus according to the present invention which provides forfive cooking zones. Container 250 is adapted for accommodating hotcooking oil. The raw or partially precooked food product is introducedinto container 250 in the area indicated by arrow 251. As the foodproducts are cooked, they travel with oil through zone A and come intocontact with a rotating device such as a paddles 252 which dunks,separates, agitates and controls the advance of the food products. Therotational speed of the devices 252 is controlled to retain the foodproducts for the appropriate time as they move through zone A. Thetemperature at the beginning of zone A within the oil is determined bythe incoming hot oil entering through inlet 253 through which flow iscontrolled by valve 254. The oil entering through inlet 253 has beenheated in heat exchanger 255 and is controlled to be within atemperature range, preferably for cooking hard-bite potato chips, whichis about 300° to 310° F. As the hot oil entering through inlet 253 comesin contact with the food products the cooking process causes heattransfer from the oil to the food products, driving off moisture fromthe food products. Therefore the time-temperature profile of the cookingoil in zone A as it moves, as shown from left to right, is steadilydecreasing since no new heated oil is injected along the cooking path inzone A, the maximum temperature within zone A occurs at inlet 253 andthe minimum temperature within zone A occurs just prior to inlet 256which also marks the beginning of zone B. Hot oil may then be introducedthrough inlet 256 controlled via valve 257. The oil entering throughinlet 256 is intended not to elevate the temperature of the oil at thatpoint but rather to change the rate of temperature drop within zone B.Hence within zone B the temperature of the oil just following inlet 256will be less than temperature of the oil immediately preceding inlet256. The cooking food products are advanced through zone B by way ofdevice 257 to rotate, control and dunk product. At the end of zone B isa sump 258 where oil can be withdrawn via outlet 259. As shown, the oilprior to being withdrawn through outlet 259 is filtered through afiltering means such as an endless mesh belt 260 continuously rotatedaround drums 261. Alternatively a perforated drum may be used as thefiltering means such as that illustrated and described in connectionwith FIG. ID above. Also located at sump 258 is oil inlet 262 controlledby valve 263. By controlling the rate of withdrawing of oil throughoutlet 259 and introducing of hot oil into inlet 262 it is intended thatthe fresh oil cause a surge such that the temperature at inlet 262 andjust subsequent thereto will exhibit a rise in temperature. The rate ofintroducing the hot oil is such that the temperature will rise withinzone C peaking prior to the end of zone C and cooling prior to sump 264.In a typical hard-bite chip cooking process the temperature near sump258 will be approximately 245° to 255° F. with the temperature peakingwithin zone C at about 260° and then cooling to about 255° at sump 264.The cooked food products are driven through zone C with a flightedsubmerger conveyor belt 265 similar to belt 15 shown in FIG. 2 above. Atsump 264 there is an outlet 266, an inlet 267 controlled by valve 268and a perforated drum filtering mechanism 269. The perforated drumfiltering mechanism 269 is similar to that described in FIG. ID above.Inlet 267 marks the beginning of zone D in which the time-temperatureprofile will be similar in shape to that of the time-temperature cookingprofile of zone C, i.e., there will be an initial surge in temperaturepeaking before the end of zone D and cooling prior to reaching sump 270.At sump 270 there is again an outlet 271, an inlet 272 controlled byvalve 273 similar to that shown in connection with sump 264. There isalso a drum filtering mechanism 274 similar to that shown in connectionwith FIG. ID above. A flighted submerger conveyor belt 275 drives thecooked food products through zone D. In zone E the food products aredriven via flighted submerger conveyor belt 276 and the withdrawal ofoil through outlet 271 and introduction of hot oil through inlet 272 iscontrolled so that the time-temperature cooking profile is similar inshape to that of zone C and D, i.e., there is initial temperature surgepeaking prior to the end of zone E and cooling by the time the end ofzone E is reached. The final temperature attained at the end of zone Efor cooking hard-bite chips is approximately 300° to 310° F. with theoverall temperature increasing in steps from sump 258 to the end of zoneE, as will be described in further detail below in connection with FIG.6. The cooked food products are withdrawn from the oil baths viaconveyor belt 277 and directed to further processing, as needed. Otherfeatures of FIG. 5 show withdrawal of oil via terminating sump 278through outlets 279. All of the withdrawn oil from outlets 259, 266, 271and 279 may be recirculated to heat exchanger 255 via pump 280. Somerecirculated oil can be continuously filtered through filter 281 andpumped back through pump 280 to withdraw fines suspended in the oilprior to being heated in heat exchanger 255 for reintroduction into thecontainer 250. Bypass line 282 may be utilized to insure the proper flowcharacteristics through the heat exchanger 255. As shown the container250 is enclosed within hood 283, for reasons discussed above inconnection with hood 80 described in FIG. 1. The hood 283 is vented witha vent 284. The flow of oil to pump 280 is through a continuous finesremoval device, such as a motorized catch-box 285.

Referring to FIG. 6 there is shown a plot of a typical time-temperaturecooking profile for cooking hard-bite chips in a five zone cookingapparatus such as that described in FIG. 5. As shown in the figure thefood products enter the oil at the beginning of zone A at a temperatureof about 305° F. Throughout zone A the temperature steadily drops, notnecessarily at a constant rate to an end point of about 250° F. New oilis added to lessen the rate of cooling, however there is no temperaturerise during zone B which begins after two minutes of cooking time. Atthe end of about four minutes of cooking time the cooked products enterzone C at the beginning of which there is both withdrawal andintroduction of hot new oil at a beginning temperature of about 240° F.The temperature rises at the beginning of zone C, peaks before the endof zone C and then cools to a temperature at the end of zone C at about255° F. Then oil is withdrawn and hot oil introduced such that thetemperature again begins to rise at the beginning of zone D, peakingbefore the end of zone D and cooling to the end of zone D to atemperature at about 275° F. Oil is again withdrawn and hot oilintroduced to again produce a surge in the temperature peaking beforethe end of zone E and cooling at the end of zone E to about 295° F. atwhich point the cooked food products are withdrawn. The total cookingtime as shown is about ten minutes wherein the food products spend onaverage about two minutes in each of zones A, B, C, D and E.

Referring to FIG. 7 there is shown a time-temperature profile forcooking hard-bite chips in a seven zone cooker. The first two zones Aand B are identical to that of zones A and B of FIG. 6. The onlydifference in FIG. 7 is that the remaining about six minutes of cookingtime is divided into five zones of approximately equal lengths of timerather than the two or more zones as shown in FIG. 6. Again each of thelast five zones shows a similar time-temperature cooking profile of aninitial increase in temperature, followed by peaking and a slight dropbefore reaching the end of the zone where hot oil is added to providethe desired time-temperature cooking profile for the next zone. Througheach of the zones C, D, E, F and G the temperature is gradually risingwith intermittent peaks with cooling prior to the end of each zone.

Referring to FIGS. 8 and 9, there are shown other exemplarytime-temperature cooking profiles which may be achieved in a five-zonecooker according to the present invention.

It will be readily apparent that various modifications may be made to bewithin the scope of the present invention. In particular, it may bereadily appreciated by those skilled in the art from the abovedescription that the apparatus according to the invention provideadjustability not only in time-temperature cooking profile, but also inmaximum and minimum cooking temperatures. This feature of adjustabilitycan be readily utilized to accommodate the cooking requirements of newsnack foods, such as chocolate-coated chips, grain chips, vegetablesnacks and so forth.

What is claimed is:
 1. An apparatus for continuous cooking of foodproducts comprising a container for containing a liquid cooking medium,conveying means for transporting food products along a predeterminedpath through said cooking medium, said path defined, in order by aplurality of cooking zones comprising a first zone commencing at a firstinlet for introducing oil into said bath and ending at a second inletalong said path for introducing oil into said bath, a second zonecommencing at said second inlet and ending at a first set of inlet andoutlet means for withdrawing and introducing oil from and to said bath;and two or more contiguous successive zones, respectively beginning andending with a set of inlet and outlet means for withdrawing andintroducing oil into said bath, wherein each said inlet and outlet meansis located within a sump dividing adjacent zones, and each of said sumpsaccommodates a filtering means for separating food products from oilentering said sump.
 2. An apparatus according to claim 1 wherein saidsump in which said first set of inlet and outlet means is locatedaccommodates filtering means comprising an endless mesh belt.
 3. Anapparatus according to claim 1 wherein at least one of said filteringmeans comprises a perforated drum.